Method and composition for fixing transfer image



3,929,727 METHGD AND CQMPUfiiTIGN FOR FG TRANFER IMAGE My present invention which is a continuation-in-part of my patent application Serial No. 485,805 (now abandoned) filed February 2, 1955, relates to a novel method and composition for the fixing of a transfer image in order that it may be suitable for use in connection with lithographing processes;

One of the well known copying processes of the prior art involves the transfer of an image comprising a tannableffpolloid such as a photographic gelatin emulsion by pressure to paper or any other suitably receptive medium. ",A typical process of the type to which I refer is described in United States Patent No. 2,596,756. In the operation of such copying processes, a piece of specially prepared image-receptive paper is coated with a colloid containing a light sensitive material, such as a gelatinosilver halide. This treated paper is then placed in con- .tact with the front of a sheet carrying printed matter. As

light is passed through the sheet to be copied, the exposed areas of the colloid are hardened or tanned by the action of the light, while the non-exposed image areas are not so hardened and may then be transferred by pressure to other sheets of paper. In the above mentioned process, it has been found desirable in order to effectively transfer the unhardened image area by pressure, to first soften it by means of an activator which may comprise a solution of containing a mixture of sodium carbonate and urea.

Prior to my invention, it has been necessary to go through a rather difficult and complicated procedure to utilize this transferred image in a paper base lithographing plate. After transfer of the image, the plate would have to be processed by three distinct steps, namely, hardening the image under light, treatment of the hardened image with pyrogallic acid, and then neutralization with acetic acid. The purpose of such a procedure was to harden the image which had been transferred to the litho graphing plate and thereby make the image more inkreceptive than the non-image area.

The reason for making the image ink-receptive is that the art of planographic printing depends upon the immiscibility of grease and water and upon the preferential retention of a greasy image-forming substance by the image areas, and a similar-retention of an aqueous dampening fluid by the non-image areas. When a greasy image is imprinted upon a suitable surface, and the entire surface is then moistened with an aqueous solution, the image areas-will repel the water, and the non-image areas will retain the water. Upon subsequent application of greasy ink, the image portions retain the ink, whereas, the moist, non-image areas repel it. The image is then transferred to paper or cloth, via an intermediary, so called off-set cylinder, which is necessary to prevent mirror image printing.

I propose to provide a novel composition which will in a single step, make the light-sensitive colloid transfer image hereinbefore referred to grease receptive and hence suitable for use in a planographic printing process.

Accordingly an object of my invention is to provide a novel fixing composition which will provide an ink receptive transfer image for lithographing.

' Another object of my invention is to provide a method 2 for producing in a simple operation, a suitable paper base planographic printing table to which an image comprising a tannable colloid has been transferred by pressure.

These and other objects of my invention will become more apparent from the following description.

The novel fixer which I propose for the image which is trnsferred by pressure to the paper base lithographing I plate comprises an aqueous solution containing, in combination, a tanning agent, a substance to make the image ink or grease receptive and a buffer to maintain the pH of the solution within proper limits.

The tanning agent includes tannic, gallic or pyrogallic acid in combination with a water soluble trivalent salt such as the soluble salts of aluminum, chromium and trivalent iron. The buffer may include a polybasic water soluble organic acid which does not form a precipitate with a trivalent salt cation.

the buffer may comprise an acid salt mixture such as a mixture of phosphoric acid and monobasic ammonium phosphate.

The image is made grease or ink receptive by including in the aqueous solution of water soluble alcohol or sugar derivative. For this purpose it is particularly preferred to use ethylene glycol or other water soluble polyhydric alcohols such as the following:

From the above it can be seen that the polyhydric alcohols within the scope of the preferred embodiment of the present invention include alcohols and derivatives thereof containing not more than six carbon atoms.

Other alcohols which may be used, but are less elfective, are water soluble alcohols containing a single hydroxy group and having a chain length of not more than three carbon atoms. These are made up of the group consisting of methyl, ethyl, isopropyl and 'N-propyl alcohols.

Also sugars and sugar derivatives may be used, examples of which are sucrose, mannitol and sorbitol.

It is essential to include one or more of the above compounds for the purpose of bringing out the image and making it grease receptive. It is recognized that the prior art discloses many applications of tannic acid etches including gum or gum derivatives therein. These etches are used for desensitizing purposes, for cleaning the background of a lithographing plate and very often are sulficiently strong to tend to blind the image. According to my invention, however, by including a polyhydric alcohol with the tanning agent, it is possible to rather unexpectedly obtain a sensitization of the image.

Specific solutions which I prefer to employ are as follows:

Patented Apr. 17, 1962 Such acids would include oxalic, maleic, malonic and citric acids. Alternatively,-

III

Water -2 Q. ml 75 Ethylene glycol ml Oxalic acid g 10 A1Cl g 1 Tannic acid -u a g 1 IV Water ml 75 1,3-butylene glycol ml 20 Oxalic acid g 10 Alclg g 1 Tannic acid g l Water ml 75 Ethanol ml" 15 Oxalic acid g 10 Ferric chloride g l Pyrogallic acidg 1 Water ml 80 Sorbitol g 10 1 Maleic acid V g 12 Ferric chloride v g 1 Gallic acid g 1 It is to be understood that in the above specific formulations the other alcohols or sugar derivatives hereinabove referred to may be substituted in substantially the same proportions as indicated for the ethylene glycol or 1,3-butylene glycol. Moreover, other salts of the type hereinabove referred to may be substituted for aluminum or ferric chloride. More specifically, some of the salts would include other soluble ferric salts such as ferric nitrate, and soluble chromic salts such as chromic chloride. Moreover, aluminum sulphate or aluminum nitrate may be substituted for the aluminum chloride, although aluminum chloride is my preferred embodiment.

While the proportions above indicated are to be preferred, it is to be understood that the range of proportions may vary considerably. Thus, the amount of water soluble alcohol or sugar derivative may be between 10 and percent by volume. The buffer whether it be a mixture of monobasic ammonium phosphate and phosphoric acid, or one of the Water soluble dibasic acids listed above, should be so adjusted as to result in a pH of between 1.5 and 2.5.

Ordinarily, the trivalent salt and tanning acid should be added in approximately equal amounts. Thus, in

Examples I and 11 using aluminum chloride and tannic acid, each is present in an amount between 4 percent and 10 percent by weight and preferably between 0.5 and Spercent.

One type of planographic printing plate to which the image may be applied comprises a paper plate treated with a Water repellent coating such as urea-formaldehyde mixture. The Water-proofed paper is then covered with a hydrophilic layer. A particularly suitable hydrophilic layer comprises a mixture of starch carbamate and a filler and/or pigment such as clay and/or titanium dioxide. The type of plate to which I refer is described for example, in my copending application Serial No. 490,268, filed February 24, 1955, now U.S. Patent No. 2,766,688, issued October 16, 1956. W

The soft non-ink receptive image comprising a nonhardened light sensitive colloid such as a silver bromidegelatin mixture is transferred by pressure to the paper lbase planographic printing plate. Upon treatment of this plate with my novel fixing composition, the image is made highly ink receptive in a manner not heretofore realized by the prior art. No hardening step by exposure to light or by any other method is necessary to convert the image to an ink-receptive state. Thus, not only are the complicated procedures of the prior art avoided, but

an image having superior qualities of ink receptiveness is formed. An image of high ink receptivity on the lithographing plate not only means that a sharper print is obtained, but also that even before the image is transferred to the lithographing plate, the exposure time in the copying process becomes less critical.

In the foregoing, I have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specific disclosure herein, but only by the appending claims.

I claim:

1. A composition for fixing a gelatino-silver halide image on a lithographic plate comprising an aqueous solution of a water soluble trivalent salt, a tanning agent from the group consisting of tannic, gallic and pyrogallic acids in combination with a substance for making the image grease receptive from the group consisting of polyhydric alcohols having not more than six carbon atoms, monohydric alcohols having not more than three carbon atoms, and sucrose.

2. A composition for fixing a gelatino-silver Blalide image on a paper base lithographic plate and making such image grease receptive comprising an aqueous solution including a water soluble trivalent salt, a tanning agent from the group consisting of tannic, gallic and pyrogallic acids, a polyhydric alcohol containing not more than six carbon atoms, and a buffer adapted to maintain the pH of said aqueous solution between 1.5 and 2.5.

3. The composition of claim 2 in which the buffer comprises a polybasic acid from the group consisting of oxalic acid, maleic acid, malonic acid and citric acid.

4. The composition of claim 2 in which the buffer comprises a mixtureof monobasic ammonium phosphate and phosphoric acid.

5. A composition for fixing a gelatino-silver halide image on a paper base lithographic plate and making such image grease receptive comprising an aqueous solution including a water soluble trivalent salt from the group consisting of aluminum, ferric and chromic salts, a tanning agent from the group consisting of tannic, gallic and pyrogallic acids, from 10 to 30 percent by volume of a polyhydric alcohol containing not more than six carbon atoms, and a buffer adapted to maintain the pH of said aqueous solution between 1.5 and 2.5.

6. A method for making a gelatino-silver halide image transferred to a lithographic plate ink receptive, which comprises treating the said plate with an aqueous solution of a water-soluble trivalent salt, a tanning agent from the group consisting of tannic, gallic and pyrogallic acids and a member of the group consisting of polyhydric alcohols containing not more than six carbon atoms, monohydric alcohols containing not more than three carbon atoms, and sugar derivatives from the group consisting of sucrose, mennitol, and sorbitol.

7. A method for making a gelatino-silver halide image ink receptive, which comprises transferring the unhardened image to a lithographic plate and then treating the said plate with an aqueous solution comprising a water soluble trivalent salt, a tanning agent from the group consisting of tannic, gallic and pyrogallic acids, at polyhydric alcohol containing not more than six carbon atoms, and a buffer adapted to maintainthe pH of said aqueous solution between 1.5 and 2.5.

8. A method for making a gelatino-silver halide image ink receptive, which comprises transferring the unhardened imageto a lithographic plate and then treating the said plate with an aqueous solution including a water soluble trivalent salt, a tanning agent from the group consisting of tannic, gallic and pyrogallic acids, a polyhydric alcohol containing not more than six carbon atoms, and a buffer adapted to maintain the pH of said 7 aqueous solution between 1.5 and 2.5, the buffer com- THW prising a polybasic acid from the group consisting of oxalic acid, maleic acid, malonic acid and citric acid.

9. A method for making a gelatino-silver halide image ink receptive, which comprises transferring the unhardened image to a lithographic plate and then treating the said plate with an aqueous solution including a water soluble trivalent salt, a tanning agent from the group consisting of tannic, gallic and pyrogallic acids, a polyhydric alcohol containing not more than six carbon atoms, and a buffer adapted to maintain the pH of said aqueous solution between 1.5 and 2.5, the said bufier comprising a mixture of monobasic ammonium phosphate and phosphoric acid.

10. A method for making a gelatino-silver halide image ink receptive, which comprises transferring the unhardened image to a lithographic plate and then treating the said plate with an aqueous solution including a water soluble trivalent salt from the group consisting of aluminum, ferric and chromic salts, a tanning agent from the group consisting of tannic, gallic and pyrogallic acids, from to 30 percent by volume, of a. polyhydric alcohol containing not more than six carbon atoms, and a buffer adapted to maintain the pH of said aqueous solution between 1.5 and 2.5.

11. A composition for fixing a gelatino-silver halide image on a lithographic plate comprising an aqueous solution of tannic acid, aluminum chloride, and ethylene glycol.

12. A composition for fixing a geiatino-silver halide image on a lithographic plate comprising an aqueous solution of tannic acid, aluminum chloride, and ethylene glycol and a butler adapted to maintain the pH of said aqueous solution between 1.5 and 2.5.

13. A method for making a gelatino-silver halide image ink receptive, which comprises transferring the unhardened image to a lithographic plate and then treating the plate with an aqueous solution of a water soluble trivalent salt, tanning agent from the group consisting of tannic, gallic and pyrogallic acids in combination with a substance for making the image grease receptive from the group consisting of polyhydn'c alcohols having not more than six carbon atoms, monohydric alcohols having not more than three carbon atoms, and sucrose.

14. A method for making a gelatino-silver halide image ink receptive, which comprises transferring the unhardened image to a lithographic plate and then treating the plate with an aqueous solution comprising tannic acid, aluminum chloride and ethylene glycol.

15. A method for making a gelatino-silver halide image ink receptive, which comprises transferring the unhardened image to a lithographic plate and then treating the plate with an aqueous solution comprising tannic acid, aluminum chloride and ethylene glycol and a butter adapted tomaintain the pH of said aqueous solution between 1.5 and 2.5.

References Cited in the file of this patent UNITED STATES PATENTS 1,574,356 Beebe Feb. 23, 1926 1,618,505 Beebe et al. Feb. 22, 1927 2,192,482 Schroeder Mar. 5, 1940 2,231,045 Wood Feb. 11, 1941 2,229,051 Dell June 21, 1941 2,393,875 Van Dusen Jan. 29, 1946 2,503,679 Newman Apr. 11, 1950 2,515,536 Van Dusen July 18, 1950 2,704,712 Jackson Mar. 22, 1955 2,763,553 Clark et a1. Sept. 18, 1956 

1. A COMPOSITION FOR FIXING A GELATINO-SILVER HALIDE IMAGE ONA LITHOGRAPHIC PLATE COMPRISING AN AQUEOUS SOLUTION OF WATER SOLUBLE TRIVALENT SALT, A TANNING AGENT FROM THE GROUP CONSISTING OF TANNIC, GALLIC AND PYROGALLIC ACIDS IN COMBINATION WITH A SUBSTANCE FOR MAKING THE IMAGE GREASE RECEPTIVE FROM THE GROUP CONSISTING OF POLYHYDRIC ALCOHOLS HAVING NOT MORE THAN SIX CARBON ATOMS, MONOHYDRIC ALCOHOLS HAVING NOT MORE THAN THREE CARBON ATOMS, AN SUCROSE. 